1. Field of the Invention
The present invention relates to improved hydrogenation catalysts, a method of producing such catalysts, and to the production of gamma-butyrolactone with such catalysts from maleic acid, succinic acid, maleic acid, succinic acid, maleic anhydride, succinic anhydride, and mixtures thereof, and, more particularly, relates to highly selective hydrogenation catalysts comprising elemental Cu-Pd or Cu-Pt, a method of producing such catalysts, and an improved process for the production of gamma-butyrolactone by catalytically hydrogenating, in the vapor phase, a feed compound selected from the group consisting of maleic acid, succinic acid, maleic anhydride, succinic anhydride, and mixtures of any of the foregoing with or without butyrolactone, in the presence of said highly selective hydrogenation catalysts.
2. Description of the Prior Art
Gamma-butyrolactone is a stable, well known compound that is a liquid at - 44.degree. C. to 204.degree. C. It is preferably used as an intermediate, e.g., in the manufacture of 2-pyrrolidone, .alpha.-tetralone, glutaric acid, etc. It is also useful in the solvent welding of plastic films; as a swelling agent for cellulose acetate films; and as a non-corrosive solvent for polymers in general, acetylene, and water-immiscible alcohols.
In general, the catalytic hydrogenation of maleic anhydride and/or other related compounds to produce gamma-butyrolactone (hereinafter referred to as "butyrolactone") is an old and well established art for which a great many processes have been used, the most important of which historically have been effected in the liquid phase.
Exemplary of such liquid phase processes are U.S. Pat. Nos. 2,772,291-3, which generally relate to high pressure hydrogenation of maleic anhydride to form various mixtures of butyrolactone, tetrahydrofuran, and butanediol in the presence of such catalysts as those of nickel-chromium-molybdenum, Raney-type nickel or cabalt, and nickel or cobalt molybdates. Later patents utilizing liquid phase, catalyst hydrogenation of conventional feedstocks, such as maleic anhydride, to butyrolactone have substantially dealt with modifications of those types of catalyst. For example, U.S. Pat. No. 3,312,718, relating generally to substantially complete conversion of succinic anhydride to butyrolactone, employs a hydrogenation catalyst, preferably of nickel, along with a silicotungstic acid as promoter.
Additionally, U.S. Pat. No. 3,113,138 discloses processes utilizing palladium catalysts, in the liquid phase, together with certain solvents, to obtain butyrolactone from succinic anhydride, but processes such as these have been characterized by a short catalyst life and have been unable to provide adequate yields.
An alternative to the commercially-used, liquid phase catalytic hydrogenation of maleic anhydride, succinic anhydride, etc., feedstocks essentially consists of vapor phase hydrogenation, at low pressures, in the presence of a generally different class or type of catalyst, but there has been much less activity in this area in general, and processes using vapor phase catalytic hydrogenation have not heretofore found commercial favor. Exemplary of patents covering vapor phase catalytic hydrogenation of conventional feedstocks to butyrolactone include, for example, U.S. Pat. No. 3,065,243, wherein the conversion to butyrolactone is effected at low pressure in the presence of a copper chromite catalyst. Later work in this field has included various catalyst modifications utilizing, e.g., different combinations of copper, chromium, and zinc, whereby, in some instances, Cu-Zn has been used; in other instances, a combination of Cu-Cr has been used; and, finally, in another combination, that of Cu-Cr-Zn has been used. Exemplary of this later work is U.S. Pat. No. 3,580,930, which describes the use of Cu-Cr-Zn.
In addition, among other conventional hydrogenation catalysts, there may be mentioned catalysts containing such metals as rhenium and rhodium, but neither of these is presently used for hydrogenation reactions of the type described herein and neither would be as acceptable as the catalysts previously described above.
However, commercial practice in respect of the production of butyrolactone from conventional maleic anhydride, succinic anhydride, etc., feedstocks by catalytic hydrogenation has not been entirely successful, especially in terms of both high activity and high yield. The present invention has been developed to fill this void, and provides elemental Cu-Pd and Cu-Pt catalysts, which not only retain the selectivity shown by copper alone without additives, but also have an activity much greater than that afforded by copper alone.